(a) Field of Invention
The present disclosure of invention relates to digital-to-analog converters (DAC) and particularly to those used for receiving digital input signals operating at a first voltage range and outputting corresponding analog signals to display devices such as Liquid Crystal Displays (LCD's) operating across a wider second voltage range.
(b) Description of Related Art
Recently, flat panel displays such as organic light emitting devices (OLED's), plasma display devices (PDP's), liquid crystal display (LCD's), etc., have been actively developed for replacing the conventionally heavy and large cathode ray tube (CRT) as a form of display, particularly in digital display applications.
The typical PDP uses plasma generated light based on electrically driven gas discharge for displaying characters or images. The typical OLED displays characters or images by using field emission of a particular organic material or polymer. In the LCD, an electrical field is applied to a liquid crystal layer interposed between two display substrates, and transmittance of light passing through the liquid crystal layer is controlled by controlling strength of an electrical field between the substrates to thus obtain a desired image. Voltages used in each of these applications varies according to the underlying technology and according to the interface technologies used for interfacing control electronics (i.e., logic) with drive electronics (i.e., output buffers).
Among the above mentioned flat panel displays, the LCD and the OLED for example, typically include a display substrate on which pixel areas are formed to include switching elements (i.e., thin film transistors) and display signal lines. The typical flat panel also includes a gate-lines driver for transmitting binary gate signals to gate lines that are provided crossing with the display signal lines for turning the switching elements of the pixel areas on or off. The typical flat panel also includes a gray voltages generator for generating a plurality of gray level analog voltages to be used for driving pixel areas at different light intensities. The typical flat panel also includes a data driver for selecting voltages corresponding to video data among the gray voltages as data voltages and applying the selected data voltages to the data lines, and a signal controller for controlling them.
The data driver typically includes a plurality of data driving ICs, and each data driving IC (monolithic integrated circuit) includes a shift register, a latch, a digital-to-analog converter (DAC), and an output buffer.
The typical DAC may convert a digital data signal operating at a first voltage range (i.e., 0-5 volts) into an analog data signal operating across a second and different voltage range (usually larger, i.e., 0-10 volts) by using at least two different power supplies for providing respective low and high power voltages, VDD and VDDH for the digital logic and digital drive circuits. Yet a third power supply is typically provided for supplying the analog voltages used in directly driving the display mechanism (e.g., LCD or PDP). In respect to providing interfacing between logic signaling that operates from the first power voltage, VDD and drive signaling that typically operates from the second and higher power voltage, VDDH, such typically requires use of a DC-to-DC converter type of power supply that generates the second higher power supply voltage, VDDH from the first VDD. It additionally calls for level shifting circuits for converting digital signals operating in the first signaling range (i.e., 0-5V) to the second one (i.e., 0-10V). Use of such additional circuits may lead to an increase in area used by the logic and driving circuits and an increase in power consumption.